First, this approach is a hypothesis! I am not sure about the aperture or if this will help to increase the sampling and speed sensibility!
I used the datasheet as reference, based at the 1,275 cpi at 1mm. I calculated the size of the pixel based on the 3.5mm of the chip (I know.... the sensor and laser are smaller, etc... but just to make things easier) and calculated the size of the footprint at 30mm. This rendered approximately 120 degrees of aperture.
Using as reference the 9mm distance from the filament and opening the area only to the length of the filament, and a little to the perpendicular, i think it can increase the sensibility and give a better response to fast movements than that very tiny small window of the reference housing. Avoiding scattering of the laser will be achieved by a light sanding of the internal surfaces.
The casing is designed to with Z heights that are both 0.3mm and 0.2mm compatible.
Another hypothesis I would like to test and compare is using 0.15mm and 0.1mm as I fell that higher Z definition will help the reduce the "shineness" of the printed part.